Ernary composite material having nio nanosheet/bimetallic cecuox microsheet core-shell structure, and preparation and application thereof

ABSTRACT

Provided are a ternary composite material having a NiO nanosheet/bimetallic CeCuOx microsheet core-shell structure, and a preparation method therefor, and an application thereof. CeCuOx has a large specific surface area and high stability. A NiO/CeCuOx core-shell structured composite material catalyst is prepared by growing NiO nanosheets on the surface of CeCuOx by low-temperature hydrothermal treatment and heat treatment. The bimetallic CeCuOx microsheet shows better catalytic performance for toluene than monometallic oxides, i.e., copper oxide and cerium oxide. The further growth of the NiO nanosheets having different concentrations effectively improves catalytic activity. A 3Ni/CeCuOx catalyst can realize complete catalysis of toluene at 210° C.

TECHNICAL FIELD

The present invention relates to the technical field of nanocompositematerials, and in particular, to the preparation of a NiO nanosheet @bimetallic CeCuO_(x) microsheet core-shell structure composite materialand the application thereof in catalytic heating treatment of toluene.

BACKGROUND

A volatile organic compound (VOC) having a boiling point between roomtemperature and 260° C. is considered to be a major factor causingglobal air pollution, especially environmental pollution, such as ozone,photochemical smoke, and secondary aerosol caused by toluene. The use ofeffective techniques will reduce damage to the environment and humanhealth. Low temperature catalytic oxidation techniques are believed tobe an efficient and economical process for removing toluene, resultingin extensive search interest.

In recent years, scientists have made great efforts to develop moreefficient catalysts that can catalyze the oxidation of VOCs at lowertemperatures. Generally speaking, there are two types of highlyefficient catalysts for total VOC oxidation, which are supported noblemetal and transition metal oxide catalysts. Although noble metal-basedcatalysts are considered better catalysts for VOC catalytic oxidationand have attracted much attention, they have the disadvantages of poorthermal stability and high cost, high surface energy and easyagglomeration. Therefore, efforts are being made to design differentmulti-component transition metal oxide nanostructured catalysts, such ascore-shell structures and hollow porous materials with high surfaceareas.

Transition metal oxide catalysts are much cheaper than expensive andrare noble metals. They are viable and sufficiently active in somereactions. In order to achieve the purpose of developing alternative tonoble metal catalysts and lowering the reaction temperature, it isnecessary to conduct research on multiple transition metal oxidecatalysts. As typical transition metal oxides, CeC₂, NiO and CuO havethe advantages of low cost and high thermal stability. Therefore, inview of the current situation, it is necessary to develop an effectivemethod to prepare new multi-component composite catalysts.

SUMMARY OF THE INVENTION Technical Problem

The purpose of the present invention is to provide a NiO nanosheet @bimetallic CeCuO_(x) microsheet core-shell structure composite materialby using a water bath thermal reaction method to form a NiO nanosheetonto a bimetallic CeCuO_(x) microsheet, so as to achieve the purpose ofefficiently treating gas pollutants, such as toluene gas, at a lowtemperature.

Technical Solution

In order to achieve the above purpose, the present invention adopts thefollowing specific technical solution: a ternary NiO nanosheet @bimetallic CeCuOx microsheet core-shell structure composite material isprepared by a method that includes the following steps: (1) mixing acerium salt, a copper salt, an organic acid, and a solvent, performing asolvothermal reaction, and calcining a reaction product of thesolvothermal reaction to obtain a CeCuOx microsheet.

(2) performing a water bath reaction of a mixture of a nickel salt,urea, and the CeCuOx microsheet in an alcohol/water mixed solvent, andcalcining a reaction product of the water bath reaction to obtain theternary NiO nanosheet @ bimetallic CeCuOx microsheet core-shellstructure composite material.

Specifically, (1) dissolving a cerium salt, a copper salt andterephthalic acid in a solvent, mixing, placing the mixture into ahigh-pressure reaction kettle for a solvothermal reaction, andcentrifugally washing, drying and calcining the reaction product toobtain the CeCuOx micro-sheet.

(2) dissolving a nickel salt and urea in a mixed solution of ethanol andwater, adding CeCuOx powder for a water bath reaction, and centrifugallywashing, drying and calcining the reaction product to obtain the ternaryNiO nanosheet @ bimetallic CeCuOx microsheet core-shell structurecomposite material.

In the present invention, the cerium salt is cerium nitrate hexahydrate,and the copper salt is copper nitrate trihydrate; the solvent is DMF (N,N-dimethylformamide); the nickel salt is nickel nitrate; and in thealcohol/water mixed solvent, the alcohol is ethanol, preferably a volumeratio of alcohol and water is 1 : 1.

Preferably, in the ternary NiO nanosheet @ bimetallic CeCuOx microsheetcore-shell structure composite material, a weight of the NiO nanosheetis 1-5 times a weight of the bimetallic CeCuOx microsheet. For example,the weight ratio of the NiO nanosheet to the bimetallic CeCuOxmicrosheet is 1 : 1, 3 : 1, 5 : 1.

In the present invention, the dissolution in the solvent is at roomtemperature, a time is 2-3 hours; the solvothermal reaction is conductedin a high pressure reactor, a reaction temperature is 80° C.-90° C., areaction time is 24-25 hours, preferably, the reaction temperature is80° C., and the reaction time is 24 hours; and the calcination isperformed in air, a calcination temperature is 350° C.-400° C., acalcination time is 4-4.5 hours, preferably, the calcination temperatureis 350° C., a heating rate is 3° C./min during calcination, and thecalcination time is 4 hours.

In the present invention, the water bath reaction is conducted 80°C.-90° C., a reaction time is 1.5-3 hours, preferably at 80° C. for 2hours; the calcination is performed in air, the calcination temperatureis 350° C.-400° C., the calcination time is 4-4.5 hours, preferably, thecalcination temperature is 350° C., the heating rate is 3° C./min duringcalcination, and the calcination time is 4 hours.

In the present invention, the molar ratio of cerium salt, copper saltand terephthalic acid in step (1) is 2 : (1.0-1.1) : (4.0-4.1); in step(2), a molar ratio of nickel salt to urea is 1 : (5.0-5.1); and thenickel salt is Ni (NO₃)₂.

The present invention first uses a bimetallic metal-organic framework asa catalyst precursor to prepare a binary metal oxide catalyst havingexcellent activity (CeCuOx), which has a large specific surface area andgood stability. The large specific surface area can promote catalyticperformance, forming a good catalyst material. A nickel oxide nanosheetis then formed on the surface of the CeCuOx by a low-temperature waterbath heating and heat treatment method, and preparing the yNiO/CeCuOxcore-shell structure composite material catalyst with different ratiosby adjusting a mass ratio of NiO/CeCuOx. The NiO nanosheet forms on thebimetallic CeCuOx microsheet, obtaining a morphology, further increasingthe contact area. The catalytic active site is increased, the catalyticeffect is improved, and the method is efficient and economical.

After calcination treatment, an amount of NiO nanosheet @ bimetallicCeCuOx microsheet core-shell structure composite material is placed intoa toluene environment with a certain concentration, and the compositematerial is heated and catalyzed by using a fixed bed reactor, so thatlow-temperature catalytic oxidation of toluene is realized. GCMS-QP 2020test shows that toluene is completely catalyzed.

The present invention further discloses the application of theabove-mentioned NiO nanosheet @ bimetallic CeCuOx microsheet core-shellstructure composite material in low-temperature catalytic oxidation oftoluene.

In the method for low-temperature thermal catalytic treatment oftoluene, the NiO nanosheet @ bimetallic CeCuOx microsheet core-shellstructure composite material is placed in a toluene-containingenvironment, toluene treatment is completed by using a fixed bedreactor. Preferably, the temperature of the low-temperature completecatalytic oxidation of toluene gas is 210° C.

Beneficial Effect

The advantages of the present invention: 1. the NiO nanosheet @bimetallic CeCuOx microsheet core-shell structure composite materialdisclosed by the present invention has a large surface area, a uniformpore size, and a controllable structure. The growth of the nickel oxideincreases the oxygen vacancy and contact area of the carrier, whichsignificantly improves the catalytic performance of the carriercatalyst. The nanosheet grows uniformly on the bimetallic CeCuOxmicrosheet to form a core-shell structure, so that the large specificsurface area can promote the catalytic performance, increase thereaction active site. It is a good multi-element transition metal-typecatalyst material.

2. According to the method of preparing the NiO nanosheet @ bimetallicCeCuOx microsheet core-shell structure composite material disclosed bythe invention, the loading of noble metal particles is avoided, the costof the material is greatly reduced, and the nickel oxide grows on theCeCuOx microsheet nanosheet, so that the experimental process isrelatively simple, the catalytic performance on toluene is excellent.Therefore, the NiO nanosheet @ bimetallic CeCuOx microsheet core-shellstructure composite material has high economic practicability andresearch value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron microscope (SEM) image of a CeCuOxmicrosheet.

FIG. 2 is a transmission electron microscope (TEM) diagram of the CeCuOxmicrosheet.

FIG. 3 is a scanning electron microscope (SEM) of the 3Ni/CeCuOxcore-shell structure composite material.

FIG. 4 is a transmission electron microscope (TEM) diagram of the3Ni/CeCuOx core-shell structure composite material.

FIG. 5 is a graph of the thermal catalytic effect of the NiO nanosheet @bimetallic CeCuOx microsheet core-shell structure composite material ontoluene gas.

DETAILED DESCRIPTION

The preparation method of the NiO nanosheet @ bimetallic CeCuOxmicrosheet core-shell structure composite material disclosed by theinvention includes the following steps: (1) dissolving a cerium salt, acopper salt and terephthalic acid (H₂BDC) in a solvent, mixing, placingthe mixture into a high-pressure reactor, carrying out a solvothermalreaction, and carrying out centrifugal washing, drying and calciningtreatment to obtain a CeCuOx micro-sheet.

(2) dissolving a nickel salt and urea in a mixed solution of ethanol andwater, adding CeCuOx powder to conduct a reaction heating with a waterbath, and then centrifugal washing, drying, and calcining to obtain theNiO nanosheet @ bimetallic CeCuOx microsheet core-shell structurecomposite material.

The starting materials used in the present invention are conventionalcommercially available, and the preparation method and test method areconventional methods in the art.

Example 1: the preparation of CeCuOx including the following steps:dissolving Ce(NO₃)₃·6H₂O (0.868 g, 2 mmol) and Cu(NO₃)₂·3H₂O (0.242 g, 1mmol) in DMF (40 mL) at room temperature, and stirring at 1000 rpm for 2h; dissolving H₂BDC (0.664 g, 4 mmol) in DMF (40 mL), and stirring at1000 rpm for 2 h. The two solutions were then mixed with ultrapure water(20 mL) in a stainless steel autoclave, thermally reacted at 80° C. for24 hours, washed several times with DMF and ethanol, then dried undervacuum at 65° C. for 6 h, and then calcined at 350° C. in air for 4 h,increasing the heating temperature from room temperature to 350° C. at arate of 3° C./min to obtain the CeCuOx microsheet. FIG. 1 is an SEMimage of a CeCuOx microsheet, and FIG. 2 is a TEM image of the CeCuOxmicrosheet; and it can be seen from figures that the microsheet has atwo-dimensional layered structure, a regular parallelogram morphology.

Example 2: the preparation of the ternary NiO nanosheet @ bimetallicCeCuOx microsheet core-shell structure composite material include thefollowing specific steps: an amount of nickel oxide being 3 times ofCeCuOx, dissolving Ni(NO₃)₂ and urea in a molar ratio of 1: 5 in a 100mL water/alcohol of 1/1 volume ratio, adding 100 mg of prepared CeCuOxmicrosheet powder, and reacting the obtained solution at 80° C. for 2hours under stirring. The reaction mixture was filtered and washed, thendried at 90° C. and calcined at 350° C. under an air atmosphere at aheating rate of 3° C./min for 4 h to obtain a ternary NiO nanosheet @bimetallic CeCuOx microsheet core-shell structure composite material,named as 3Ni/CeCuOx (representing the weight ratio of NiO nanosheet tobimetallic CeCuOx microsheet of 3: 1), and performance andcharacterization testing were performed.

FIG. 4 is an SEM image of the 3 Ni/CeCuOx composite material, and FIG. 5is a TEM image of the 3Ni/CeCuOx composite material. It can be seen fromthe figures that the nickel oxide successfully grows on the CeCuOxmicrosheet, and the distribution is uniform.

The amount of Ni(NO₃)₂ was changed to obtain materials with the weightratio of NiO nanosheet to the bimetallic CeCuOx microsheet being 1 : 1,5: 1, named as NiCeCuOx, 5NiCeCuOx, respectively.

Example 3: the thermal catalytic condition of the p-toluene gas by theternary NiO nanosheet @ bimetallic CeCuOx microsheet core-shellstructure composite material was that the toluene concentration is 50ppm (air is used as a filling gas, purchased from Messer Air Liquide Co.Ltd.), the amount of the catalyst was 50 mg, the catalyst was fixed on afixed bed reactor through a U-shaped pipe according to a conventionalmethod, the catalytic effect of the composite material on toluene gasunder the heating condition was analyzed through gas chromatography, andthe test condition was 36000 ml (h·g).

FIG. 5 is a graph of the thermal catalytic effect of the ternary NiOnanosheet @ bimetallic CeCuOx microsheet core-shell structure compositematerial on toluene gas. As shown in FIG. 5 , the present invention canbe applied to conversion of toluene at lower temperatures. Toluenepollution in air is mainly derived from building materials, indoordecorative materials, living and office supplies, outdoor industrialwaste gas, automobile exhaust, photochemical smoke and the like, and thetoluene specific catalytic effect is analyzed by gas chromatography, andthe toluene conversion rate calculation method is shown in equation (1):

$\eta = \frac{C_{o} - C}{C_{o}} \times 100\%$

C₀ and C are the initial concentration and test concentration of toluenein the experiment, respectively (tested once every 15 minutes).

As shown in the comparative results of FIG. 5 , the catalyticperformance of the bimetallic CeCuOx sample with large sheet morphologyis obviously superior to that of a single metal CeO₂ and CuO sample, andthe advantages of the bimetallic sample morphology structure are proved.In addition, nickel oxide is grown on the CeCuOx microsheet, so that theconcentration of oxygen vacancies is further improved, the catalyticperformance is obviously improved, the uniform growth of nickel oxidealso greatly improves the catalytic performance of the nickel oxide, andthe use of noble metals is avoided. Therefore, the 3Ni/CeCuOx compositecatalyst is relatively economical and efficient.

Comparative Example: performing the solvothermal synthesis at 80° C. inthe preparation example C for 24 hours was changed to performing thesolvothermal synthesis at 80° C. for 48 hours, and the remainingconditions were unchanged. CeCuOx was obtained. Microsheet was preparedaccording to the method of Example 2. 3Ni/CeCuOx was prepared. The sametoluene conversion test was performed. Toluene gas cannot be completelycatalyzed at 210° C., i.e., the conversion rate is less than 100%.

The heating rate of 3° C./min in Example 1 was changed to 10° C./min.The remaining conditions were unchanged. CeCuOx microsheet was preparedaccording to the method of Example 2. 3Ni/CeCuOx was prepared. The sametoluene conversion test was performed. The conversion rate was less than95% at 210° C.

The temperature 350° C. in Example 2 was changed to 400° C. Theremaining conditions were unchanged. 3Ni/CeCuOx was prepared. The sametoluene conversion test was performed. The conversion rate was less than92% at 210° C.

Comparative Example: dissolving Ni(NO₃)₂ and urea in a molar ratio of 1:5 in a 100 mL solution having a water/alcohol volume ratio of 1/1, thenplacing the obtained solution under conventional stirring at 80° C. for2 reaction hours, drying at 90° C., calcining at 350° C. in an airatmosphere at a heating rate of 3° C./min to obtain a solid material,performing the same toluene conversion test, and converting being lessthan 30% at 210° C.

By analyzing the above experiments, it is indicated that the nickeloxide nanosheet using the technical solution of the present inventioncan successfully grow to the CeCuOx microsheet to form a core-shellstructure composite material. The process is simple and feasible, thegrowth of nickel oxide is very uniform, and the composite material in acertain proportion has a relatively good catalytic activity for toluene.The NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structurecomposite material has a relatively large specific surface area, auniform pore size and a controllable structure; the growth of nickeloxide increases the oxygen vacancy and contact area of the carrier,which significantly improves the catalytic performance of the carriercatalyst; and the nanosheet grows uniformly on the bimetallic CeCuOxmicrosheet to form a core-shell structure. The large specific surfacearea can promote the catalytic performance, increase the reaction activesite, and be a good multi-element transition metal-type catalystmaterial. Meanwhile, the loading of noble metal particles is avoided,the cost of the material is greatly reduced, the experimental process isrelatively simple, and the catalytic performance on toluene isexcellent, so that the catalyst provided by the invention furtherrealizes the purpose of economic practicability.

1. A ternary NiO nanosheet @ bimetallic CeCuOx microsheet core-shellstructure composite material, wherein the ternary NiO nanosheet @bimetallic CeCuOx microsheet core-shell structure composite material isprepared by a method comprising the following steps: (1) mixing a ceriumsalt, a copper salt, an organic acid, and a solvent, performing asolvothermal reaction, and calcining a reaction product of thesolvothermal reaction to obtain a CeCuOx microsheet; (2) performing awater bath reaction of a mixture of a nickel salt, urea, and theCeCuO_(x) microsheet in an alcohol/water mixed solvent, and calcining areaction product of the water bath reaction to obtain the ternary NiOnanosheet @ bimetallic CeCuO_(x) microsheet core-shell structurecomposite material.
 2. The ternary NiO nanosheet @ bimetallic CeCuOxmicrosheet core-shell structure composite material according to claim 1,wherein in step (1), a molar ratio of the cerium salt, the copper saltand the organic acid is 2 : (1.0-1.1) : (4.0-4.1); the solvent is DMF;and the organic acid is terephthalic acid.
 3. The ternary NiO nanosheet@ bimetallic CeCuOx microsheet core-shell structure composite materialaccording to claim 1, wherein Ce(NO₃)₃· 6H₂O, Cu(NO₃)₂·3H₂O are used asstarting materials, and the CeCuOx microsheet is prepared in thepresence of terephthalic acid.
 4. The ternary NiO nanosheet @ bimetallicCeCuOx microsheet core-shell structure composite material according toclaim 1, wherein in step (2), a molar ratio of the nickel salt to ureais 1 : (5.0-5.1), and the nickel salt is Ni(NO₃)₂.
 5. The ternary NiOnanosheet @ bimetallic CeCuOx microsheet core-shell structure compositematerial according to claim 1, wherein in the ternary NiO nanosheet @bimetallic CeCuOx microsheet core-shell structure composite material, aweight of the NiO nanosheet is 1-5 times of a weight of the bimetallicCeCuOx microsheet.
 6. A method of preparing the ternary NiO nanosheet @bimetallic CeCuOx microsheet core-shell structure composite material ofclaim 1, comprising the following steps: (1) mixing a cerium salt, acopper salt, an organic acid, and a solvent, performing a solvothermalreaction, and calcining a reaction product of the solvothermal reactionto obtain a CeCuOx microsheet; (2) performing a water bath reaction of amixture of a nickel salt, urea, and the CeCuO_(x) microsheet in analcohol/water mixed solvent, and calcining a reaction product of thewater bath reaction to obtain the ternary NiO nanosheet @ bimetallicCeCuO_(x) microsheet core-shell structure composite material.
 7. Themethod of preparing the ternary NiO nanosheet @ bimetallic CeCuOxmicrosheet core-shell structure composite material according to claim 6,wherein in step (1), a reaction temperature of the solvothermal reactionis 80° C.-90° C., and a raction time is 24-25 hours; the calcination isperformed in air, a calcination temperature is 350° C.-400° C., and acalcination time is 4-4.5 hours.
 8. The method of preparing the ternaryNiO nanosheet @ bimetallic CeCuOx microsheet core-shell structurecomposite material according to claim 6, wherein in step (2), a reactiontemperature of the water bath reaction is 80° C.-90° C., and a ractiontime is 2-2.5 hours; the calcination is performed in air, a calcinationtemperature is 350° C.-400° C., and a calcination time is 4-4.5 hours.9. An application of the ternary NiO nanosheet @ bimetallic CeCuOxmicrosheet core-shell structure composite material of claim 1 in alow-temperature thermal catalytic treatment of a gas pollutant.
 10. Theapplication of claim 9, wherein the gas pollutant is toluene.